1. Field of the Invention
The present invention relates to an horizontal articulated robot, and more particularly, to a structure of mounting portions of an end effector mounted at the extreme end of a robot arm.
2. Description of the Related Art
Horizontal articulated robots, which are also called scalar robots, are excellent particularly in compactness and workability and often used in industrial robots. The horizontal articulated robot has such a structure that ordinarily, first and second arms turn each in a respective horizontal plane through first and second joint shafts, respectively and an end effector such as a hand and the like is mounted on a working shaft attached to the extreme end of the second arm to thereby cause the end effector to execute a desired job such as an assembly, transport, and the like of a work (refer to, for example, Japanese Unexamined Patent Application Publications Nos. 2000-24966 and 11-301813). In this case, in the robot shown in the patent document 1, the upper surface of a second arm acts as a mounting portion for transporting a work, and, in the robot shown in the patent document 2, the lower surface of a second arm acts as a mounting portion for assembling and transporting a work.
As described above, in the conventional horizontal articulated robots, the mounting portion of a hand or a work is disposed only to one side (upper or lower side) of the second arm, that is, an extreme end arm. When, for example, a job for transferring a wafer, a glass substrate, and the like is executed, an end effector such as a hand and the like must be mounted on the upper side of the extreme end arm. On the other hand, when assembly, transport, and the like of parts are executed, the end effector must be mounted on the lower side of the extreme end arm. Accordingly, a type of a robot and a mounting method must be changed in conformity with a work transport form, a type of a work, and the like. As a result, in a conventional robot system, there is a possibility that different types of robots are mixedly used depending on types of work transport forms and types of works.
Further, in a robot having such a structure that wiring or piping ducts of a drive unit for driving an end effector, a working shaft, and the like are exposed in the periphery of arms, the robot is bad in an outside appearance as well as the layout of the wiring or piping ducts must be determined such that the motion of the arms is not restricted by the ducts and that the ducts do not interfere with an external object and the like.
An object of the present invention, which was made in view of the above problems, is to provide a horizontal articulated robot that can cope with various work transport forms and various types of works by one type of a robot by selectively using the upper and lower ends of a working shaft.
Further, an object of the present invention is to provide a horizontal articulated robot that minimizes the externally exposed portions of wiring or piping of a drive unit of an end effector, a working shaft, and the like as well as does not restrict the motion of arms and does not have a possibility of interfering with an external object and the like.